Return on investment is a performance measure used to evaluate the efficiency of a project or to compare the efficiency of a number of different projects. ROI measures the amount of return on a project relative to its cost. To calculate ROI, the return (net benefit: benefit minus cost) of a project is divided by the cost of the project, with the result expressed as a percentage. The requirement of benefit to be expressed in money terms is the main reason that ROI (or cost-benefit analysis) is not used extensively in health technology assessment, however it is used in other contexts such as planning large capital investments (new hospitals, units or services).